Abstract
The soy compound genistein has been observed preclinically to inhibit bladder cancer growth with one potential mechanism being the inhibition of epidermal growth factor receptor phosphorylation (p-EGFR). A phase 2 randomized, placebo-controlled trial investigated whether daily, oral genistein (300 or 600 mg/d as the purified soy extract G-2535) for 14 to 21 days before surgery alters molecular pathways in bladder epithelial tissue in 59 subjects diagnosed with urothelial bladder cancer (median age, 71 years). G-2535 treatment was well tolerated; observed toxicities were primarily mild to moderate gastrointestinal or metabolic and usually not attributed to study drug. Genistein was detected in plasma and urine of subjects receiving G-2535 at concentrations greater than placebo subjects' but were not dose-dependent. Reduction in bladder cancer tissue p-EGFR staining between the placebo arm and the combined genistein arms was significant at the protocol-specified significance level of 0.10 (P = 0.07). This difference was most prominent when comparing the 300-mg group with placebo (P = 0.015), but there was no significant reduction in p-EGFR staining between the 600-mg group and placebo. No difference in normal bladder epithelium p-EGFR staining was observed between treatment groups. No significant differences in tumor tissue staining between treatment groups were observed for COX-2, Ki-67, activated caspase-3, Akt, p-Akt, mitogen-activated protein kinase (MAPK), or p-MAPK. No significant differences in urinary survivin or BLCA-4 levels between treatment groups were observed. Genistein displayed a possible bimodal effect (more effective at the lower dose) on bladder cancer tissue EGFR phosphorylation that should be evaluated further, possibly in combination with other agents.